Production of Ester-Based Fuels Such As Biodiesel From Renewable Starting Materials

ABSTRACT

Production of ester-based fuels such as biodiesel or jet fuel from renewable starting materials such as lignocellulosic material or algae is disclosed. Pulping and saccharification of the renewable starting materials produces carboxylic acids such as fatty acids or rosin acids, which are esterified via a gas sparged, slurry form of heterogeneous reactive distillation to yield ester-based fuels.

This application claims the benefit of priority to U.S. patentapplication Ser. No. 12/172,649, filed Jul. 14, 2008, which claims thebenefit of priority to U.S. Provisional Patent Application 60/968,222,filed Aug. 27, 2007. The contents of each of the applications areincorporated by reference in their entirety.

FIELD OF INVENTION

A method for the production of biodiesel and other ester-based fuels,such as jet fuel, from renewable starting materials such as whole plantoils is disclosed. In one embodiment, esterification of carboxylic acidsrecovered from pulping and saccharification of cellulosic material orother renewable starting material is accomplished via a gas sparged,slurry form of heterogeneous reactive distillation.

BACKGROUND

One area of interest for its ability to produce a net reduction inlifecycle carbon emissions comes in the form of alcohols produced byfermentation. Fermenting soluble sugars to produce ethanol or butanol isknown in the art. While fermentation of soluble sugars may represent away to energy self sufficiency for petroleum-challenged regions, the netlifecycle carbon dioxide emissions may actually exceed those ofpetroleum diesel and gasoline depending on the source of sugar and themethod of its fermentation. For example, there is some debate as towhether ethanol produced from the fermentation of soluble sugars in corngrain consumes more carbon based energy than it produces. Not only is agreat deal of fossil energy expended during the planting and harvestingof grain corn, but large amounts are required during the manufacture ofethanol—especially due to the water/alcohol separation and byproductdrying steps. Furthermore, carbon dioxide is a significant byproduct offermentation itself. High soluble sugar content materials such as sugarbeets and cane can increase net energy and carbon efficiency only tosome degree.

One approach to achieving positive net energy production is to convertinsoluble sugars such as cellulose from widely available lignocellulosematerial to soluble sugars that can be fermented. For example, theproduction of corn grain also yields a comparable amount oflignocellulosic material that is currently underutilized. The yield ofgrain ethanol from corn grain is about 29 wt %. The mass of corn stoverto grain is roughly 1:1 and processes for recovering 20 wt % ethanolfrom stover have been commercialized. Converting the cellulose in stoverto soluble sugar (a process known as saccharification or hydrolysis)consumes additional energy relative to that of simply tilling the stoverback into the ground. However, the 70% increase in ethanol productioncompensates for the additional energy requirements causing the overallprocess to become respectably net energy productive.

The US Departments of Agriculture and Energy have estimated that thecurrent availability of corn stover for use in ethanol production,without any change to current tillage or land use practices, to be about75 million tons. If other lignocellulosic crop wastes are considered,the available cellulose from current agricultural practices is in excessof 190 million tons per year (Table 3). (U.S. Department of Agricultureand U.S. Department of Energy. BIOMASS AS FEEDSTOCK FOR A BIOENERGY ANDBIOPRODUCTS INDUSTRY: THE TECHNICAL FEASIBILITY OF A BILLION-TON ANNUALSUPPLY”. April, 2005.) If no-till practices are adopted and crop yieldsincreased, the amount of biomass available for fuel production can beincreased to approximately 500 million tons per year (Table 4). Furtherexpansion of available biomass to nearly a billion tons per year isachievable by increased farming of perennials such as switch grass(Table 5).

Forestry offers another source of cellulose for the production ofethanol. The US Departments of Agriculture and Energy have estimatedthat the current availability of cellulose from forest resources standsat 142 million tons per year and is expandable to 368 million tons peryear (Table 6).

Underutilized cellulose from agriculture and forestry represents aresource for the production of net energy positive ethanol. Assuming the1 billion tons per year or so that USDA and DOE estimate to be withinreach along with a 20 wt % yield leads to over 60 billion gallons ofethanol production per year with a net reduction in CO₂ production.These resources can be realized only if the sugars locked in biomass inthe form of insoluble cellulose can be separated from associated ligninand transformed into soluble sugar via saccharification/hydrolysis.Diverse technologies for accomplishing this separation exist at varyingstages of investigation or commercialization. (“Costs ProhibitCellulosics Use as Feedstock”. C&EN, Apr. 12, 1976, pg. 12.)

Despite the investigation of ethanol as an alternative to petroleum toreduce carbon emissions, there remains a need for economically-viableenergy alternatives such as plant and animal-derived ester-based fuelsfor controlling carbon dioxide emissions during the production ofenergy.

SUMMARY OF INVENTION

One object of the invention is to convert the fatty acid form of lipidsthat are liberated during the hydrolysis and saccharification oflignocellulosic material or other renewable starting material to esterbased fuels. According to the invention, a process for the production ofester-based fuel from renewable starting material comprises: i)comminution of renewable starting material; ii) isolation of celluloseand other soluble and insoluble sugars, including isolation byhydrolysis and/or saccharification of the comminution product; iii)isolation of fatty acid and/or rosin acid; iv) addition of a C1-C8alcohol to the fatty acid and/or rosin acid and esterification; and v)refining of the resulting ester to produce an ester-based fuel.According to one embodiment of the current invention, step iv of theinvention is accomplished via the esterification method disclosed inU.S. Pat. No. 5,536,856 (Harrison et al.) which is utilized to esterifyfatty and/or rosin acids with normal and branched alcohols with 1 to 8carbons.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an overall sequential block diagram of the invention utilizinggravity settling.

FIG. 2 is an overall sequential block diagram of the invention utilizingliquid-liquid extraction.

FIG. 3 is a schematic of batch extraction.

FIG. 4 is a schematic of continuous extraction.

FIG. 5 categorizes various methods of cell disruption for comminution ofstarting material.

FIG. 6 is an overall sequential block diagram of the embodiment of theinvention as it applies to production of fuel esters from algae usingalkali lyses.

FIGS. 7 a and 7 b are Table 1, which list potential oil yield data fromlignocellulose materials.

FIG. 8 is Table 2, which categorizes several methods of concentratingmicro algae.

FIG. 9 is Table 3, which is the available cellulose from currentagricultural practices under certain conditions.

FIG. 10 is Table 4, which is the amount of biomass available for fuelproduction under the listed conditions.

FIG. 11 is Table 5, which is the available biomass achievable byincreased farming of perennials such as switch grass.

FIG. 12 is Table 6, which is the current availability of cellulose fromforest resources.

DETAILED DESCRIPTION OF INVENTION

Lipids are contained by all living cells as an energy store and arecomponents of all living cell membranes. Typically, lipids produced forenergy storage are in the form of glycerides while those found in cellmembranes are in the form of phospholipids. In either case, the cellulardestruction objective and the harsh conditions of the hydrolysis andsaccharification technologies to achieve it also liberate cellularlipids in their glycerol- and phosphorous-free forms—i.e. as fattyacids. Such fatty acids can be converted into ester-based fuels.Producing energy from plant and animal-derived ester-based fuelsrepresents one means of controlling carbon dioxide emissions during theproduction of energy due to reduction in net carbon emissions over thecycle of production and use associated with these materials. Forexample, soy biodiesel was shown to reduce net carbon emissions by 78%over petroleum diesel. (U.S. Department of Agriculture and U.S.Department of Energy. Life Cycle Inventory of Biodiesel and PetroleumDiesel for Use in an Urban Bus. May 1998.)

The present invention improves upon the prior art by increasing thefeedstock pool available for the production of ester fuels byapplication of fatty and/or rosin acid technologies developed for Kraftprocessing. Utilizing an almost completely overlooked, enormous supplyof fatty and/or rosin acids promises to greatly expand the renewabletransportation fuel pool. The present invention also improves upon theprior art by supplying an esterification method that is more efficient,less polluting, and less capital intensive than transesterificationprocesses used to convert glycerides to esters. The esterificationprocess of the invention also greatly improves upon other wet chemicaland heterogeneous esterification technologies by avoiding soapformation, overcoming equilibrium constraints, simplifying alcoholrecovery, permitting online catalyst change out, and utilizing real-timedynamic and steady state optimization to manage optimization of catalystusage, energy consumption, and feedstock costs.

Selection and Comminution of Renewable Starting Material

According to the invention, the first step in a process according to theinvention involves selection of a renewable starting material asfeedstock for the process. Selection of the renewable starting materialinvolves an evaluation of cost of the starting material and estimationof yield of final product.

Materials destined for cellulosic ethanol production have beenevaluated, and found to contain low relative concentrations of fattyacids. As a result, it is unlikely that many of these materials willever be grown purely for that content. Rather, it will be theircellulose content that leads to byproduct fatty acid production.Relative to the amount of ethanol produced, the amount of fatty acidbyproduct is actually quite significant. Assuming a typical yield of 20%ethanol and 2% fatty acid means that a minimum of 10% of an ethanolproducer's high value products could be in the form of fatty acids.

Distillers dried grains with solubles (DDGS), the “other” product ofcorn grain fermentation, also contain a significant amount of lipids.Belyea et al. found 12 wt % “fat” on average and a maximum of 15.2 wt %.(Belyea, R. L., et al. “Composition of corn and distillers dried grainswith solubles from dry grind ethanol processing”. BioresourceTechnology, 94 (2004), pp. 293-298; Belyea, R. L., et al. “Variabilityin the Nutritional Quality of Distillers Solubles”. BioresourceTechnology, 66 (1998) pp. 207-212.) However, because the grain corncontains ample soluble sugar, the process for liberating them is notharsh enough to render the fats in their fatty acid form. Rather, thefat from DDGS is predominantly in the glyceride form. The form of lipidcontent is included in the initial evaluation of the economic potentialfor a feedstock material.

According to the current invention, making use of DDGS for additionalethanol production rather than treating it as a byproduct would involveprocessing it in a way similar to other lignocellulosic materials. Indoing this, the ethanol producer would gain additional ethanol yield andavoid handling and distribution costs involved in marketing DDGS. Itwould also result in conversion of the triglyceride lipids in DDGS totheir fatty acid form thereby producing an ideal feedstock according tothe esterification method of the invention.

One source of data useful in estimating potential yields of fatty acidsfrom the hydrolysis of other lignocellulosic materials is laboratoryexperiments dedicated to the elucidation of the lipid composition ofwhole plant material. For example, Dien, B. S. et al. studied thecomposition of liquors produced by dilute acid pretreatment andenzymatic saccharification of alfalfa, reed canarygrass, andswitchgrass. (Dien, B. S., et al. “Chemical composition and response todilute-acid pretreatment and enzymatic saccharification of alfalfa, reedcanarygrass, and switchgrass”. Biomass and Bioenergy, 30 (2006), pp.880-891.) They obtained maximum ether extracted fatty acid yields of 0.9wt %, 2.2 wt %, and 1.6 wt % for alfalfa, reed canarygrass, andswitchgrass respectively. Another source of potential oil yield datafrom lignocellulose materials comes in the form of livestock feedstuffanalysis. Typical data where fat is expressed as “ether extractives” isgiven in Table 1.

Some possible starting materials are listed in Table 1, such as wheatstraw, rice straw, rapeseed, rapeseed plant, field pennycress, Jatropha,mustard, flax, sunflower, canola, palm, hemp, cotton plant, sunflowerplant, peanut, tobacco, sugarcane, sugarbeet, potatoes, sorghum, barley,oats, beans, hardwood, softwood, pine wood, forest products, woodresidues, coconut copra, alfalfa, canarygrass, switchgrass, soy plant,soy bean, corn, corn grain, corn stover, and any other startingmaterials, as desired.

In one economically important field, the yield of fatty acids from Kraftprocessing of pine wood is known to be in the range of 15-20 kg/ton ofdry wood. Even with Kraft pulping there is room for improvement. Onlyapproximately 45% of CTO (crude tall oil) available in the pine tree isrecovered. The rest is lost during woodyard operations (20%), pulping(15%), black liquor recovery (15%), and acidulation (5%). Severalprocessing changes have been proposed to improve this yield. Forinstance, woodyard operations have become more efficient, with aturnover of one week, as opposed to two months, when these numbers wererecorded. This has compensated for CTO losses that resulted from anincreased use of hardwood. CTO losses due to soap adsorption on the pulpcan be reduced, too. In a 1400 t/d pulp mill, about 25 t/d of soap isleft on the pulp. Much of this soap can be recovered by addingN,N-dimethyl amides of tall oil fatty acids to the wash water of therotary drum vacuum filter in the third and final pulp washer stage.Also, the addition of 6-7 grams of propyl stearic amide to the washsystem per ton of pulp has been reported to increase tall oil soapyields significantly. (Huibers, D. (Union Camp Corporation). Tall Oil.Kirk-Othmer Encyclopedia, John Wiley and Sons, 1996.)

Because most other hydrolysis processes and lignocellulosic sources areexperimental, thinly commercialized, and lacking in optimization, it israre to find literature dedicated to the concept of the recovery offatty and/or rosin acids as byproducts from them. This is somewhatsurprising given the potential 1.5-2.0 wt % yield of fatty acids impliedby pine wood. Simple translation of this yield to the current unutilizedportion of agricultural waste lignocellulose is equivalent toapproximately 1 billion gallons pr year of ester fuels. Furthermore, itis well known that certain crop wastes have several times the potentialfatty acid yield of pine wood.

As an alternative to crop waste, single celled plants such as bacteria,algae, and yeasts offer another underutilized source of lipids fromwhich fatty acids can be recovered in much the same way as withlignocellulosic materials. Algae, in particular, produce and utilizelipids in much the same way as plants. Like plants, they have toughouter coatings that contain phospholipid chains. They also producetriglycerides as an energy store. Also like plants, they can be readilygrown in enormous, outdoor farms. While yeast and bacteria are usedcommercially to produce a variety of fine chemicals such as alcohols,acetone, proteins, and insulin, use of algae to produce large quantitiesof lipids is a new industry.

Algae come in both prokaryotic (bacteria like) and eukaryotic (plant andanimal like) forms. What distinguishes algae is that they are one celledor multicellular organisms capable of performing photosynthesis yetlacking in leaves, roots, flowers, seeds, and other organs. Prokaryoticcyanobacteria, such as spirulina or blue-green algae, are considered tobe half bacteria and half algae. Eukaryotic algae have decidedlyplant-like cell structures and can even assemble into structures such askelp, also known as brown algae, and seaweed, also known as green algae,that resemble whole plants. The different levels of organization ofalgae cells are as follows:

-   -   Colonial—small, regular groups of motile cells    -   Capsoid—individual non-motile cells embedded in mucilage    -   Coccoid—individual non-motile cells with cell walls    -   Palmelloid—non-motile cells embedded in mucilage    -   Filamentous—a string of non-motile cells connected together,        sometimes branching    -   Parenchymatous—cells forming a thallus with partial        differentiation of tissues

Algae tend to produce lipids with high degrees of unsaturation. (Evans,R. W. et al. “LIPID COMPOSITION OF HALOTOLERANT ALGAE, DUNALIELLA PARVALERCHE AND DUNALIELLA TERTIOLECTA”. Biochemica et Biophysica Acta, 7 12(1982), pp. 186-195.) Most algae are strictly autophototropic, derivingenergy from photosynthesis. Some forms are mixotropic and can deriveenergy from both photosynthesis and uptake of carbon molecules.Commercial growing of Algae is accomplished in systems that providewater for suspending the algae, light, nutrients, and carbon dioxide.These so called photobioreactors take on a variety of forms. (Forexample, see Rorrer, G., Mullikin, R. “Modeling and simulation of atubular recycle photobioreactor for macroalgal cell suspensioncultures”. Chemical Engineering Science 54 (1999) pp. 3153-3162.)

According to the current invention, algal paste concentrates are lysedwith alkali and heat to saponify the fats and lipids contained withinthe cells. The saponified fatty acids are recovered by phase separation(skimming) from the cooking liquor and acidulated to yield free fattyacids. These fatty acids are then esterified according to theesterification method of the invention. Also according to the currentinvention, algal paste concentrates are lysed with acids and the fattyacids are recovered via phase separation. These fatty acids are thenesterified according to the esterification method of the invention.

Delignification in the Production of Ester-Based Fuels

Once a renewable starting material is chosen as the feedstock for aprocess according to the invention, the starting material is processedto separate out the fatty acid. For lignocellulosic starting materials,processing includes removal of the lignocellulose. This processing stepmay be informed by processes used in ethanol production and paperpulping.

The goal of freeing cellulose from its lignin matrix (i.e. pulping) iscommon to both ethanol production and paper making. Large-scale ethanolproduction seeks to further transform liberated cellulose intowater-soluble sugars via staged operations. These goals are similar tothat of paper making and recovery of fibers from lignocellulosicmaterials. The main difference between paper making and ethanolproduction has to do with the final disposition of cellulose. With papermaking, the goal is to recover as high of a yield of clean, i.e.lignin-free, cellulose fibers as possible. With ethanol production,lignin-free cellulose is an intermediary material which must be furthertransformed into soluble sugars such as glucose. This extra step isknown as saccharification or hydrolysis.

The overall process from lignocellulosic fiber to soluble sugar usuallyfollows a sequence beginning with some form of mechanical comminution,followed by chemical and/or hydrothermal pulping and delignification(hydrolysis), and followed by further saccharification. While theydiffer in terms of the specific pulping, delignification, andsaccharification methods, the harsh conditions used in these processesall liberate the fats, and other potential sources of ester-basedbiofuels contained in plant matter, as carboxylic acids rather thanglycerides.

It is possible to group technologies into classes. Each class can beused alone or in combination with another class to effect thetransformation of the cellulose in lignocellulose material to solublesugar as part of the process of separating out fatty acids:

-   -   1. Alkaline Solution Pulping (Kraft)    -   2. Dilute Acid Pulping    -   3. Concentrated Acid Pulping    -   4. Organic Solvent Pulping    -   5. Hydrothermal Pulping    -   6. Ammonia, or Carbon Dioxide Pulping    -   7. Wet Oxidation Pulping    -   8. Enzymatic Hydrolysis    -   9. Bacterial Digestion

A commercial process for pulping of biomass which already produces abillion pounds per year of carboxylic acids suitable for use in thepresent invention is known as the Kraft process. Kraft processing is amajor source of paper pulp. Kraft processors normally utilize some formof mechanical reduction of plant mass (wood) such as grinding, followedby treatment of the plant mass with heat and a solution of water, strongbase, and Na₂S (also known as white liquor) in order to separatecellulose from lignin. (Sell, J. N., Norman, J. C., “Chemical andPhysical Properties of High-Yield Alkaline Sulfite Green Liquor”. Ind.Eng. Chem. Res. 32 (1993), pp. 2794-2199.) During Kraft pulping, theresin and fatty acids in the wood are saponified into soaps. Thesolution of these soaps along with lignin is known as black liquor.(Wagner, C. L. “Alkali Recovery from Pulp Liquors by a ChemicalEngineering Process”. Industrial and Engineering Chemistry, Vol. 22, No.2, (February 1930), pp. 122-127.)

Black liquor is separated from the desired cellulose fiber byfiltration. Acidifying black liquor with sulfuric acids causes the fattyand/or rosin acid soaps contained in black liquor to precipitate out asa separate, oily phase. This oily phase is then recovered by physicalmeans, such as skimming, as “tall oil”. Tall oil can be furtherprocessed by distillation to produce pure rosin acid, fatty acid,sterol, and ester products. (Huibers, D. (Union Camp Corporation). TallOil. Kirk-Othmer Encyclopedia, John Wiley and Sons, 1996.) The rosin andfatty acids thus produced from pine wood feedstock make excellentfeedstocks for the esterification method of the present invention due totheir high degree of unsaturation. High unsaturation leads to esterfuels with exceptional low temperature properties.

While fatty and/or rosin acids produced from the Kraft process aresuitable, other pulping and delignification processes may also yieldcarboxylic acids suitable for the production of biofuel esters. Thesemethods may be classified as mechanical, chemical, semi-chemical,hydrothermal, or enzymatic processes. (Kadla, J. and Qizhou, Dai,(University of British Columbia). Pulp. Kirk-Othmer Encyclopedia, JohnWiley and Sons, Vol. 21, 2006; Mabee, W. E., et al. “Updates onSoftwood-to-Ethanol Process Development”. Applied Biochemistry andBiotechnology, Vol. 129-132 (2006), pp. 55-70; Mohanty, B. “Technology,Energy Efficiency and Environmental Externalities in the Pulp and PaperIndustry”. Asian Institute of Technology, 1997.)

Alkaline solution pulping is the most prevalent today. Kraft or Sulfitepulping accounts for most alkaline pulping performed commercially. Soda,and Soda-anthraquinone are other examples of water based, alkalinepulping. (Sun, R. C., et al. “Structural and physico-chemicalcharacterization of lignins solubilized during alkaline peroxidetreatment of barley straw”. European Polymer Journal, 38 (2002), pp.1399-1407.) Xylan Inc. discloses an alkaline pulping process thatutilizes extrusion and hydrogen peroxide. (Dale, M. C. “The XylanDelignification Process for Biomass Conversion to Ethanol.” PaperPresented at the 17^(th) Annual Biotechnology for Fuels and ChemicalsSymposium, Vail, Colo., May, 1995.) Aronovsky and Gortner published aseries of articles in the 1930's detailing various alkaline and acidic“Cooking Processes”. (Aronovsky, S. I., Gortner, R. A. “The CookingProcess I—Role of Water in Cooking Wood”. Industrial and EngineeringChemistry, Vol 22, No. 3 (March 1930), pp. 264-274.)

Pulping with dilute acid solutions is practiced. (Hakansson, H.,Ahlgren, P., “Acid hydrolysis of some industrial pulps: effect ofhydrolysis conditions and raw material”. Cellulose, Vol. 12 (2005), pp.177-183.) U.S. Pat. No. 5,705,369 discloses a process whereby solublesugars are recovered by passing a weakly acidic solution through solidcellulosic material and recovering the sugars from the filtrate. U.S.Pat. No. 6,228,177 (Torget) discloses a process whereby dilute acid isused in several stages for the hydrolysis and fractionation of biomass.U.S. Pat. No. 6,423,145 (Nguyen et al) discloses a process wherebybiomass hydrolysis is accomplished with dilute acid and a metal saltcatalyst. Alternatively, aqueous or supercritical CO₂ may be used. See,for example, U.S. Pat. No. 2,232,331, which discloses a process whereCO₂ is introduced to soap solutions at 50 atmospheres both with andwithout various solvents either miscible or immiscible in water. Seealso U.S. Pat. No. 4,495,095, which employs multiple rounds of contactbetween supercritical CO₂ and tall oil solution.

Pulping with concentrated acid solutions is also practiced. (Harris, E.E. “Wood Saccharification.” In Advances in Carbohydrate Chemistry, Vol4, Academic Press, New York, 1949, pp 153-188.) U.S. Pat. Nos. 5,562,777and 5,580,389 (Farone & Cuzens) disclose a strong acid hydrolysis methodof obtaining soluble sugars from rice straw and other lignocellulosicmaterial. In this process, soluble sugars are recovered from pulpingliquor by adsorption. The sugar free liquor is then recycled for use inthe hydrolysis steps.

Organic solvents are also employed along with these more conventionalprocesses. Examples include ASAM (alkaline-sulfite-AQ-methanol),OrganoCell (soda-AQ-methanol), or a nonconventional process, e.g.,Alcell (acid-catalyzed ALcohol-CELLulose), Acetosolv and Acetocell(acetic acid pulping), MILOX (peroxyformic acid). (Goncalves, A. R., etal. “Integrated Processes for Use of Pulps and Lignins Obtained fromSugarcane Bagasse and Straw”. Applied Biochemistry and Biotechnology,Vol. 121-124 (2005), pp. 821-826; Pan, X., et al. “Biorefining ofSoftwoods Using Ethanol Organosolv Pulping: Preliminary Evaluation ofProcess Streams for Manufacture of Fuel-Grade Ethanol and Co-Products”.Biotechnology and Bioengineering, Vol. 90, No. 4, (May 20, 2005), pp.473-481; Aronovsky, S. I., Lynch, D. F. J. “Pulping Bagasse withAlcoholic Nitric Acid Pulp Yields and Characteristics”. Industrial andEngineering Chemistry, Vol. 30, No. 7 (July 1938), pp. 790-795.) The useof ethylene glycol has been studied. (Rezzoug, S., Capart, R.“Solvolysis and Hydrotreatment of Wood to Provide Fuel”. Biomass andBioenergy, Vol. 11, No. 4 (1996), pp. 343-352; Rezzoug, S., Capart, R.“Liquefaction of wood in two successive steps: solvolysis inethylene-glycol and catalytic hydrotreatment”. Applied Energy, 72(2002), pp. 631-644; Ammar, S., et al. “Simple Mathematical Model forthe Solvolysis of Cylindrical Pine-Wood Samples”. Applied Energy, 48(1994), pp. 137-148; Thring, R. W. “Recovery of a Solvolytic Lignin:Effects of Spent Liquor/Acid Volume Ratio, Acid Concentration andTemperature”. Biomass, 23 (1990), pp. 289-305; Bouvier, J. M., et al.“Wood Liquefaction an Overview”. Applied Energy, 30 (1988), pp. 85-98.)

A hydrothermal process known as steam explosion is considered apotential low cost pulping technique. (Garrote, G., et al. “HydrothermalProcessing of Lignocellulosic Materials.” Holz als Roh- und Werkstoff 57(1999) pp. 191-202; Bonini, C., D'Auria. M. “Degradation and recovery offine chemicals through singlet oxygen treatment of lignin”. IndustrialCrops and Products. 20 (2004), pp. 243-259; Garrote, G., et al.“Autohydrolysis of agricultural residues: Study of reaction byproducts”.Bioresource Technology, 98 (2007), pp. 1951-1957; Shahbazi, A., et al.“Application of Sequential Aqueous Steam Treatments to the Fractionationof Softwood”. Applied Biochemistry and Biotechnology, Vol. 121-124(2005), pp. 973-987; Marchessault, R. H., et al. “Characterization ofaspen exploded wood lignin”. Can. J. Chem., Vol. 60 (1982), pp.2372-2382.) It involves treatment of wood or other fiber with highpressure, saturated steam for a period of time followed by suddenpressure letdown. As a result of the sudden letdown, the steamimpregnated fiber cells expand rapidly and “explode” releasing therechemical constituents. Only a small amount of lignin becomes watersoluble during steam explosion. Post treatment with 0.1M aqueous alkalisolution or organic solvents is required to dissolve water insolublelignin. Variations on the concept where CO₂ or NH₃ are used in place ofsteam are also practiced. (Sun, Y., Cheng, J. “Hydrolysis oflignocellulosic materials for ethanol production: a review”. BioresourceTechnology. 83 (2002) pp. 1-11; Mes-Hartree, M., et al. “Comparison ofsteam and ammonia pretreatment for enzymatic hydrolysis of cellulose”.Appl Microbiol Biotechnol (1988) 29, pp. 462-468; Garrote, G., et al.“Autohydrolysis of corncob: study of non-isothermal operation forxylooligosaccharide production”. Journal of Food Engineering, 52 (2002),pp. 211-218; Kim, T. H., et al. “Pretreatment of corn stover by aqueousammonia”. Bioresource Technology, 90 (2003), pp. 39-47.)

Hydrothermal treatment in combination with oxygen in a process known as“Wet-Oxidation” is also receiving attention. Variations on this processinclude the use of catalytic amounts of metal salts such as ferric orcupric sulfate, alkaline conditions, and thermophilic, anaerobicbacteria. (McGinnis, G. D., et al. “Biomass Pretreatment with Water andHigh-pressure Oxygen. The Wet-Oxidation Process”. Ind. Eng. Chem. Prod.Res. Dev. 1983, 22, pp. 352-357; Klinke, H. B., et al. “Characterizationof the Degradation Products from Alkaline Wet-Oxidation of Wheat Straw”.Bioresource Technology, 82 (2002), pp. 15-26; Sun, R. C., et al.“Chemical composition of lipophilic extractives released during the hotwater treatment of wheat straw”. Bioresource Technology, 88 (2003) pp.95-101; Ahring, B. K., et al. “PRETREATMENT OF WHEAT STRAW ANDCONVERSION OF XYLOSE AND XYLAN TO ETHANOL BY THERMOPHILIC ANAEROBICBACTERIA”. Bioresource Technology, 58 (1996), 107-113; Minowa, T. et al.“Liquefaction of Cellulose in Hot Compressed Water Using SodiumCarbonate: Products Distribution at Different Reaction Temperatures”.Journal of Chemical Engineering of Japan, Vol. 30, No. 1 (1997), pp.186-190; Karagoz, S., et al. “Catalytic hydrothermal treatment of pinewood biomass: effect of RbOH and CsOH on product distribution”. J ChemTechnol Biotechnol, 80 (2005), pp. 1097-1102; McGinnis, G. D., et al.“Conversion of Biomass into Chemicals with High-Temperature WetOxidation”. Ind. Eng. Chem. Prod. Res. Dev. 1983, 22, pp. 633-636.)

Enzymatic hydrolysis has also received a good deal of attention latelysince it offers the potential of lower utility consumption over acid oralkaline hydrolysis. (Akin, D. E., et al. “Corn Stover Fractions andBioenergy”. Applied Biochemistry and Biotechnology, Vol. 129-132 (2006),pp. 104-116.) Cellulases are usually a mixture of several enzymes. Atleast three major groups of cellulases are involved in the hydrolysisprocess: (1) endoglucanase (EG, endo-1,4-D-glucanohydrolase, or EC3.2.1.4.) which attacks regions of low crystallinity in the cellulosefiber, creating free chain-ends; (2) exoglucanase or cellobiohydrolase(CBH, 1,4-b-D-glucan cellobiohydrolase, or EC 3.2.1.91.) which degradesthe molecule further by removing cellobiose units from the freechain-ends; (3) b-glucosidase (EC 3.2.1.21) which hydrolyzes cellobioseto produce glucose. In addition to the three major groups of cellulaseenzymes, there are also a number of ancillary enzymes that attackhemicellulose, such as glucuronidase, acetylesterase, xylanase,b-xylosidase, galactomannanase and glucomannanase. During the enzymatichydrolysis, cellulose is degraded by the cellulases to reducing sugarsthat can be fermented by yeasts or bacteria to ethanol. Enzymatichydrolysis has also been used in conjunction with steam (hydrothermal)treatment. (Palmarola-Adrados, B., et al. “Combined Steam Pretreatmentand Enzymatic Hydrolysis of Starch-Free Wheat Fibers”. AppliedBiochemistry and Biotechnology, Vol. 113-116, 2004, pp. 989-1002;Öhgren, K., et al. “Effect of hemicellulose and lignin removal onenzymatic hydrolysis of steam pretreated corn stover”. BioresourceTechnology, 98 (2007), pp. 2503-2510.) It along with dilute acidpretreatment have also been studied. (Dien, B. S., et al. “Chemicalcomposition and response to dilute-acid pretreatment and enzymaticsaccharification of alfalfa, reed canarygrass, and switchgrass”. Biomassand Bioenergy, 30 (2006), pp. 880-891.) U.S. Pat. Nos. 3,990,994 (Gausset al.) and 3,990,995 (Huff and Yata) disclose cellulase-basedhydrolysis processes.

The use of bacteria itself for digestion of lignocellulose is known forcoconut shells. The process designed specifically to produce oil fromdried coconut shells, also known as copra, is described by Beckman. Hedescribes a “Bacterial Oil Recovery Process” as applied to the driedshell of the coconut. (Beckman, J. W. “Recovery of Vegetable Oils andFats by a Bacterial Process”. Industrial and Engineering Chemistry, Vol.22, No. 2 (February 1930), pp. 117-118.) U.S. Pat. No. 1,698,294(Beckman) describes this process in more detail.

When algae are chosen as the renewable starting material instead oflignocellulosic material, the processing requires concentration of thealgae. The method of algae harvesting depends on the level oforganization. Seaweeds and kelp can simply be “picked”, for example,while micro algae such as diatoms, green, golden, and blue green algaemust somehow be concentrated from their dilute (typically <500 mg/L),water dispersed form to something in the range of 15% solids. Methodssuch as centrifugation, cross-flow membrane filtration, and flocculationare practiced. (Tilton, R. C., Dixon, J. K. “THE FLOCCULATION OF ALGAEWITH SYNTHETIC POLYMERIC FLOCCULANTS”. Water Research 1972. Vol. 6, pp.155-164; Rossignol, N. “Membrane technology for the continuousseparation microalgae:culture medium: compared performances ofcross-flow microfiltration and ultrafiltration”. AquaculturalEngineering 20 (1999), pp. 191-208; Fish, N. M., Lilly, M. D. “TheInteractions between Fermentation and Protein Recovery”. Biotechnology,July, 1984, pp. 623-627.) Table 2 categorizes several methods ofconcentrating micro algae.

Once the cells are sufficiently concentrated, it becomes necessary to“disrupt”, rupture, or “homogenize” them so that compounds of interestare released for recovery. When the compound of interest is a protein,enzyme, or other delicate compound, mechanical destruction methods andequipment are employed. (Chisti, Y., Moo-Young, M. “Disruption ofmicrobial cells for intracellular products”. Enzyme Microb. Technol.April, 1986, vol. 8, 194-204. Hedenskog, G., Mogren, H. “Some Methodsfor Processing of Single-Cell Protein”. BIOTECHNOLOGY ANDBIOENGINEERING, 15, pp. 129-142 (1973). Molina Grima, E., et al.“Recovery of microalgal biomass and metabolites: process options andeconomics”. Biotechnology Advances, 20 (2003), pp. 491-515.) Mechanicalmethods are characterized as employing solid or liquid shear. Examplesof solid shear equipment include the bead mill (Shutte, H. et al.“Experiences with a 20 litre industrial bead mill for the disruption ofmicroorganisms”. Enzyme Microb, Technol., March 1983, Vol. 5, pp.143-148. Currie, J. A., et al. “Release of Protein from Bakers' Yeast(Saccharomyces cerevisiae) by Disruption in an Industrial AgitatorMill”. BIOTECHNOLOGY AND BIOENGINEERING, 14 (1972), pp. 725-736), freezepress (Magnusson, K. E., Edebo, L. “Large-Scale Disintegration ofMicroorganisms by Freeze-Pressing”. BIOTECHNOLOGY AND BIOENGINEERING,18, (1976), pp. 975-986), Dyno-Mill (Marffy, F., Kula, M. “Enzyme Yieldsfrom Cells of Brewer's Yeast Disrupted by Treatment in a HorizontalDisintegrator”. BIOTECHNOLOGY AND BIOENGINEERING, 16 (1974), pp.623-634; Mogren, H. et al. “Mechanical Disintegration of Microorganismsin an Industrial Homogenizer”. BIOTECHNOLOGY AND BIOENGINEERING, 16(1974), pp. 261-274), and the Hughes press (Scully, D. B.“Thermodynamics and Rheology of the Hughes Press”. BIOTECHNOLOGY ANDBIOENGINEERING, 16 (1974), pp. 675-687). Examples of liquid shearequipment, or homogenizers, include the Manton-Gaulin APV homogenizer.(Doulah, M. S. et al. “A Hydrodynamic Mechanism for the Disintegrationof Saccharomyces cerevesiae in an Industrial Homogenizer”. BIOTECHNOLOGYAND BIOENGINEERING, 17 (1975), pp. 845-858. Mosqueira, F. G.“Characteristics of Mechanically Disrupted Bakers' Yeast in Relation toits Separation in Industrial Centrifuges”. Biotechnology andBioengineering, 23 (1981), pp. 335-343. Whitworth, D. A. et al.“Hydrocarbon Fermentation: Protein and Enzyme Solubilization from C.lipolytica Using an Industrial Homogenizer”, 16 (1974), pp. 1399-1406.)Lipids liberated by mechanical disruption of cells tend to be mainly intheir triglyceride form. That is to say, a lipid fraction isolate fromthe mechanical destruction of algal cells will have a small ratio ofacid number to saponification value.

As with lignocellulose pulping, the use of chemicals alone or incombination with mechanical methods can improve disintegration of algae.It is often suggested to simply dry, crush, and extract oil from algaeusing hexane much in the same way that oil is recovered from soybeans.(Xu, H. et al. “High quality biodiesel production from a microalgaChlorella protothecoides by heterotrophic growth in fermenters”. Journalof Biotechnology, 126 (2006), pp. 499-507. Miao, X., Wu, Q. “Biodieselproduction from heterotrophic microalgal oil”. Bioresource Technology,97 (2006), pp. 841-846.) Lysis, as chemical disruption is known, can beaccomplished by methods similar to Kraft pulping (Minowa, T. “Oilproduction from algal cells of Dunaliella tertiolecta by directthermochemical liquefaction”. Fuel Vol. 74 No. 12, (1995), pp.1735-1738) as well as enzymatically. While chemical lysis with alkalitends to damage sensitive compounds, it is very effective in obtaininghigher yields of fatty acids in their soap form. Furthermore, alkalilysing lends itself very well to large scale production. Concentratedalgae paste is simply subjected to alkali and heat much as wood fiber istreated during the Kraft process. The resulting fatty acid soaps floatto the top of the water layer along with other organics forming anorganic layer which is 30-40% fatty acids. This layer can be skimmed andacidulated to affect separation of the fatty acids as an oil layer.(Zhu, Z., et al, “Extraction of lipids from Mortierella alpina andenrichment of arachidonic acid from the fungal lipids”. BioresourceTechnology, 84 (2002), pp. 93-95. Rezanka, T. “DETERMINATION OF FATTYACIDS IN ALGAE BY CAPILLARY GAS CHROMATOGRAPHY-MASS SPECTROMETRY”.Journal of Chromatography, 268 (1983), pp. 71-78. Minowa, T., Gillan, F.T., Dunstan, G. A., et al., Orcutt, D. M., Volkman, J. K., et al.) Theprocess of saponification followed by acidulation closely resembles theway in which soapstock from palm or soybean oil is created and thenacidulated. It is also similar to how tall oil is recovered. The lipidsthus recovered will have nearly equal saponification and acid numbervalues.

Isolation of Fatty Acids

Once a conversion of cellulose to soluble sugar has been accomplished,the recovery of fatty and rosin acids from the various stages canproceed. While fatty acids, and sometimes rosin acids, can be liberatedas a result of the hydrolysis/saccharification of lignocellulosicmaterial, the optimum method for and optimum stage in the process fortheir recovery may differ. Because lipids are bound in plant cellstructures along with lignin, it is possible that the point of highestconcentration of lipids in a given hydrolysis process will be at a pointwhen the cellulose fraction is mostly lignin free.

While the various hydrolysis/saccharification processes and combinationsthereof all liberate fatty and/or rosin acids, concentrations of thesebyproducts and the form they take at different stages in the process mayvary. It is possible to propose taking advantage of the solubilitybehavior of fatty and rosin acids in their acid form to aid inisolation. Therefore, according to the current invention, phaseseparation, either in terms of gravity settling and/or rosin acids orliquid-liquid extraction, is proposed as the means of recovery of fattyand rosin acids from hydrolysis/saccharification liquors. According tothe current invention, liquid-liquid extraction can be performed inbatch or continuous fashion. According to the current invention, theextractive solvent used in liquid-liquid extractions is chosen in orderto optimize competing objectives of low solubility in pulping liquor,high affinity for fatty and/or rosin acids, high density differencebetween pulping liquor and loaded solvent, and ease and energyefficiency of solvent recovery.

Depending on whether the hydrolysis process involves alkaline or acidicconditions, the form of the lipids at this point will either be fattyacids or fatty acid soaps. Fatty acids form soaps with the cation fromalkaline salts. In this form, fatty acids have enhanced watersolubility. Furthermore, they may serve to help render lignin more watersoluble and hence easier to separate from cellulose. When conditions areacidic, the soap-free fatty acid form of lipids dominates. In this form,the fatty and/or rosin acids of interest are not water soluble.

This lack of water solubility for the fatty acid form of lipids providesthe most viable means for their recovery separate from highconcentration lignin liquors, cellulose fibers, and sugar solutions.Depending on conditions, fatty and/or rosin acids will either form aseparate liquid phase that can be “skimmed” from aqueous or organicliquors or be readily extracted there from using a water insoluble,organic solvent.

How fatty and/or rosin acids are recovered from Kraft processes providesa framework for how they can be covered by hydrolysis/saccharificationprocesses. The Kraft pulping process yields strong cellulose fibers bydigesting pinewood chips for about two hours with an aqueous mixture ofsodium hydroxide and sodium sulfide at 165-175° C. under pressure.During pulping, the 2-3% resin and fatty acids that naturally occur inresinous wood are saponified. After filtration of the fibers, pulpingblack liquor is concentrated by multistage evaporation prior to feedingto a furnace for the recovery of the sodium salts and energy values.Black liquor soap consists of the sodium salts of the resin and fattyacids with small amounts of unsaponifiables. The soap is most easilyseparated from the black liquor by skimming at an intermediate stage,when the black liquor is evaporated to 25% solids. At this solids level,the soap rises in the skimmer at a rate of 0.76 m/h. At higher solidsconcentrations, the tall oil soap is less soluble, but higher viscositylowers the soap rise rate and increases the necessary residence times inthe soap skimmer beyond 3-4 hours. The time required for soap recoverycan be reduced by installing baffles, by the use of chemicalflocculants, and by air injection into the suction side of the soapskimmer feed pump. Soap density is controlled by the rate of airinjection. Optimum results (70% skimmer efficiency) are obtained at asoap density of 0.84 kg/L (7 lb/gal). This soap has a minimum residualblack liquor content of 15%. (Huibers, D)

In essence, Kraft pulping is a form of alkaline hydrolysis that ishalted the point at which the yield of insoluble cellulose fiber and itslignin content (expressed as “kappa” number) reach an optimum value.Continuing the cooking process for longer periods of time would resultin both higher lignin removal from and conversion to soluble sugar ofcellulose fibers. In fact, certain variations of alkalinehydrolysis/saccharification essentially use Kraft pulping as a“pretreatment” step to be followed by either more alkaline or enzymaticcooking. With these processes, the tall oil recovery methods discussedabove are directly applicable.

Kraft pulping makes up approximately 95% of the pulping capacity in theUS. The lack of recovery of fatty and/or rosin acids from the next mostpracticed pulping method, Sulfite pulping, is instructive as to thestate of recovery of fatty and/or rosin acids from non-Kraft pulpingprocesses. Pearl and McCoy (1960) demonstrated that fatty and/or rosinacids can be recovered from sulfite pulping liquors via etherextraction. However, the presence of these materials in extracts wassomewhat of a surprise to them and led them to hypothesize that morecould be recovered from the mother liquor. (Pearl, I. A., McCoy, P. F.“Studies on the Chemistry of Aspenwood. VIII.′ An Investigation of theNeutral Extractives off Commercial Aspen Spent Sulfite Liquors”. J. Org.Chem, Vol. 26, pp. 550-552.)

In general, it is proposed that fatty acids, and rosin acids in the caseof some plant materials, exist in pulping liquors and can be recovered.Depending on the type of and stage in a given process, these carboxylicacids will either be in soap or acid form. They will exist, at leastpartly, in soap form when conditions are alkaline and in fatty acidform, at least partly, when under neutral or acidic conditions. Whenthey are in acid form, they will form a separate phase from an aqueousor polar organic liquor. When they are in soap form, they will tend tobe dissolved in the aqueous liquor. As in Kraft processing,concentrating a given liquor will improve the ability to recover fattyand/or rosin acids whether in soap or acid form. According to thecurrent invention, evaporative concentration of fatty and/or rosin acidcontaining liquors may be performed prior to gravity settling orliquid-liquid extraction in order to improve recovery.

When fatty and/or rosin acids are concentrated enough and in insolubleform such that they form a separate phase, they can be removed byphysical separation. This can involve simply allowing the liquids to“settle” and then skimming off the top oil layer or removing the bottomliquor layer. Various vessels designs have been used over the years toimprove separation efficiency and throughput. API and Lamella settlersare examples of the culmination of such art. U.S. Pat. No. 3,562,096(Tourtellotte) discloses the use of continuous centrifugation to affectthe physical separation between fatty acid and resin “soaps” and cookingliquor.

Liquid-liquid extraction of fatty and/or rosin acids from aqueous orpolar organic liquors is a second method available for their recovery.Extraction can be performed at various stages in a givenhydrolysis/saccharification process. It can be accomplished in bothbatch and continuous fashion using any of a number of water insolubleorganic solvents such as petroleum ether, normal, cyclo, andiso-paraffins such as n-hexane and n-octane, alpha-olefins, petroleumnaphtha, diesel, benzene, etc. The choice of solvent involvesconsiderations such as density difference between the solvent whenloaded with fatty and/or rosin acids and the depleted pulping liquor,partitioning coefficient between fatty and/or rosin acids and thesolvent and liquor, and ease of post-separation from the fatty and/orrosin acids. Post-separation methods include distillation and membraneseparation. However, while membrane separation can impart energyefficiencies related to that lost from cooling distilled solvent, it ismost likely that distillation will be required even if membraneseparation is used.

Batch extraction is normally performed by first blending a previouslyoptimized amount of the chosen solvent, either fresh or recovered, witha previously optimized amount of pulping liquor and then agitating.After some optimal time, agitation is ceased and the liquids are allowedto separate into two or more phases. Often, a middle phase (known as a“rag layer”) will form between both desirable and undesirable extractsand liquors. The upper phase will now contain the fatty and/or rosinacids dissolved in the solvent. The bottom phase is decanted either upto or past any rag layer. If the rag layer is recovered, it is mostlikely sent to separate storage for further processing or recycle. Oncethe upper phase is all that remains in the vessel, it is subjected toeither batch or continuous distillation. Batch distillation can beperformed by simply applying heat to the extraction vessel and refluxingsome of the vapor back into the vessel via a packed or trayed column orit can be accomplished in a separate vessel.

Continuous extraction is normally performed using a vertical trayedand/or packed column. Fresh and/or recovered solvent can be fed to alocation just above the bottom of the column and aqueous or polarorganic liquor is similarly fed to a location just below the top of thecolumn. Sufficient column length both below the solvent feed and abovethe liquor feed is provided to permit disengagement of the two solventsby settling. In this way, liquid drawn from the very top of the columncan be liquor free and liquor drawn from the very bottom of the columncan be solvent free. The trays and/or packing serve to increaseinterfacial area between the two liquid phases as well as to create anequilibrium staged, counter current operation.

The fatty and resin acid depleted liquor from the bottom of the columnshould be as solvent free as possible to enable further processing ordisposal in the normal fashion. Solvent choice plays an important rolein making that happen. The solvent should not be very soluble in thebottom liquor or else its loss will contribute to operating cost bothand could effect downstream processing.

According to the current invention, the extractive solvent may berecovered by separating it from product fatty and/or rosin acids bybatch or continuous distillation. The fatty and resin acid rich solventfrom the very top of the column can be fed to continuous or batchdistillation in order to recover the solvent and produce pure fattyand/or rosin acids. The fatty and/or rosin acids themselves can furtherbe separated either by action of the solvent recovery column, ifequipped to produce three or more product streams, or by an additionaldistillation step.

Some lignocellulosic materials will not yield appreciable resin acids.Those that do will yield varying amounts. According to the currentinvention, fatty and rosin acids, when they occur together may beconverted to esters in their mixed state or separated by batch orcontinuous distillation prior to separately undergoing esterification.According to the current invention, separation by distillation of fattyand rosin acids may be accomplished via a dedicated batch or continuousdistillation unit or via the solvent recovery unit if solvent extractionis utilized to extract them from pulping liquors. The decision as towhether to separate the rosin and fatty acids when they do both occurdepends on the properties desired of the final ester fuel. Rosin acidbased ester fuels have different properties than fatty acid based esterfuels. For example, rosin esters produce more particulate matter whenthey burn. Rosin esters have lower cetane numbers than fatty acidesters. However, rosin acids can serve to lower the freeze, cloud, pour,and/or cold flow plugging point of pure fatty acid ester fuels. Rosinesters can also have higher energy densities both due to their higherdensity as well as to their higher carbon and hydrogen to oxygen ratios.

Conversion of Fatty Acids to Esters

In terms of the production of ester fuels from fats and oils,manufacturers and researchers tend to focus on seed and animal basedsources of fatty acids for the production of ester based fuels. Becauseoils derived from seed and animal fats represent the largest source offatty acids and because these sources tend to produce fatty acids thatare glycerated, the vast majority of processes developed and/orcommercialized focus on processing glycerides to esters. The method ofesterification according to the present invention becomes more optimalas the feedstock contains less glycerides.

While the conversion of glycerides to esters can be catalyzed by bothacids and bases, most if not all commercial processing of glycerides toesters is done with base catalysis. Only acid catalysis can be used toconvert fatty and/or rosin acids to ester fuels because base catalystsmerely react with acids to form soaps. Very few commercial producers ofester fuels utilize wet chemical, acid catalyzed processing. This ispartly due to the typical dominance of glycerides over “free” fattyacids in readily available fat and oil feedstocks. Undesirable sidereactions between the catalyst and the unsaturated bonds in the fats andoils contaminate final ester products with undesirable anions such assulfate and chlorine. Downstream separation difficulties from theesterification reactor are caused by the combination of soaps, glycerinand excess alcohol. Recovering excess alcohol becomes difficult as soapstend to foam or form “crud” when heated to distillation temperatures andsubjected to vapor agitation. Soap produced during reaction,neutralization, or bottoms separation inevitably contaminates the finalproduct. Soap contamination of fuel esters in turn leads to poor lowtemperature performance of the fuel. Crystals form at relatively hightemperatures plugging fuel filters and forming crud in storage andtransportation tankage.

When wet chemical, acid catalyzed esterification is applied toglyceride-free fatty acids using equipment designed fortransesterification, equilibrium constraints arise due to the effect ofthe water of reaction. Lack of full conversion of fatty acids to estersdue to equilibrium constraints leads to excessive soap production duringneutralization of the reaction mixture.

By applying heterogeneous reactive distillation technology to theesterification of glyceride-free and nearly glyceride-free fatty and/orrosin acids, we have been able to completely avoid soap formation,overcome equilibrium constraints, and reduce the alcohol recovery taskto simply separating water, alcohol, and co-produced ethers.

This technology typically employs solid, acid catalysts of either theceramic or ion-exchange resin bead type. Ceramic catalysts with highacidity or ion-exchange resins impregnated with sulfuric or other acidsare typically used. Acid impregnated Ion-exchange resins display higherreactivity but suffer from a deactivation mechanism involvingglycerides. Whereas fatty and rosin acids are able to adsorb, react withmethanol, and desorb, a significant portion of any glycerides in thefeed will absorb permanently and foul the catalyst. This has economicimplications beyond catalyst life because just as the cost of glyceridesincreases as the free fatty acid content increases, the cost of fattyacids declines as the glyceride content increases. Most reactivedistillation technologies immobilize the catalyst particles in ways thatmake change out prohibitively expensive in terms of labor, equipment,materials, catalyst support equipment, and downtime to perform onanything resembling a regular basis.

Applying the gas sparged, slurry reactor variant of reactivedistillation disclosed in U.S. Pat. No. 5,536,856 (Harrison et al.)improves upon other approaches to reactive distillation by enabling theonline addition or removal of catalyst via simple operations. Theability to change out catalyst while in operation allows foroptimization of reactor performance against catalyst cost. It alsoallows for optimization of the glyceride/fatty acid cost functionagainst the catalyst life and reactor performance functions.

According to the current invention, real-time steady state and dynamicoptimization software is used to modulate manipulated variables in orderto minimize competing cost and time functions. The steady stateoptimizer considers competing, control variable objectives such ascatalyst cost, catalyst life, feed glyceride content, feed fatty androsin acid distributions, temperatures, pressures, flows, alcoholloading, and alcohol water content in developing a set of near optimumdesired setpoints for manipulated variables for which a cost function isminimized. The dynamic optimizer works to minimize the amount of timeany of the control variables are away from their desired setpointtargets by continuously modulating the manipulated variables in adecoupled, multivariable sense.

Refining of Esters

Refining of recovered esters into various ester-based fuels is the finalstep in the process according to the invention. Suitable final productsinclude ester-based fuel such as biodiesel and jet fuel. In addition,the biodiesel product may conform to industrial standards such as ASTMD-6751, or EN or IRS standards. The ester-based fuel can be optionallyfurther processed by addition to petroleum-based fuels such as petroleumdiesel or kerosene to form blends, such as B20, or may be sold as anon-blend, such as B100. In addition, processing according to theinvention can yield an ester-based fuel with low glycerin, soap,alcohol, water, or sulfur content. By low is meant less than 5% byweight, and optionally less than 1%, and optionally less than 0.1% ofany of the listed impurities, or combinations of the listed impurities.Ester-based fuels according to the invention can be processed to meetspecifications for diesel, low sulfur diesel (LSD), ultra low sulfurdiesel (ULSD), and biodiesel (BD).

EXAMPLES

The following examples are for illustrative purposes only and are notmeant to be limiting. Various embodiments of the invention wherein allcomponents listed above may or may not be used are possible under thecurrent invention.

A sequential block diagram of an embodiment of the invention where fattyand/or rosin acids are separated from pulping liquors via gravityseparation is presented in FIG. 1. The steps which alone or incombination comprise embodiments of the current invention are shown withcontinuous line outlines and grey fills. Dashed line outlines with whitefills indicate steps which can be accomplished via numerous methods thatthemselves are not specific embodiments of the invention but which, byspecific embodiments of the invention will be improved upon due toproduction of liquid ester fuels in addition to ethanol.

Referring to FIG. 1, lignocellulosic material 1 sourced fromagricultural crop and/or forestry operations is first subjected to someform of comminution 2 in order to create a free flowing, solid feed tothe hydrolysis/saccharification section 5. Thehydrolysis/saccharification operation is composed of one or acombination of stages of operations selected from those known to thoseskilled in the art. Examples of suitable classes of stages include:

-   -   1. Alkaline Solution Pulping (Kraft)    -   2. Dilute Acid Pulping    -   3. Concentrated Acid Pulping    -   4. Organic Solvent Pulping    -   5. Hydrothermal Pulping    -   6. Ammonia, or Carbon Dioxide Pulping    -   7. Wet Oxidation Pulping    -   8. Enzymatic Hydrolysis    -   9. Bacterial Digestion

Depending on the stage or stages of hydrolysis/saccharification chosen,various chemicals, water, solvents, steam, and/or enzymes 3 will also befed to the hydrolysis/saccharification section 5. The purpose of thehydrolysis/saccharification section 5 is to free cellulose from ligninand to transform cellulose into soluble sugars such as glucose. Theresulting sugar solution 6 is then mixed with yeast and/or otherfermenting organisms 7 before undergoing batch or continuousfermentation 8. Fermentation yields the desired alcohol mixed withwater. Water is separated from alcohol by use of distillation and/ormolecular sieve adsorption to yield fuel ethanol 10. Water, CO₂, andsolids 9 will also be produced. Water and solids, which include live andexpired yeast, can be recycled, sewered, or otherwise dumped. It shouldbe understood that the specific steps 1-10 can vary depending on thedesign of the fuel ethanol operation. It is not an object of theinvention to apply the embodiments of the invention to any specificseries of fuel ethanol production steps. Rather, steps 1-10 are intendedto demonstrate how the embodiments of the invention relate togeneralized fuel ethanol production from lignocellulosic feedstocks. Insome cases, the various embodiments of the invention, as shown in greyfill, depend on the specific class of fuel ethanol technologies. Suchinstances are discussed below. Ethanol produced from the residualmaterial can be used to make up a substantial amount of the C1-C8alcohol of esterification according to the invention. By substantialamount is meant greater than 25% by weight, optionally greater than 50%by weight, and optionally greater than 90% by weight in variousembodiments.

Depending on the stage or stages of hydrolysis/saccharification chosenfor the hydrolysis/saccharification section 5, one or more streams of“pulping liquor” 11 containing liberated fatty and/or rosin acids willbe created. This stream or streams may contain varying amounts of fattyand/or rosin acids in either acid or soap form. It may have acidic,neutral, or alkaline pH. It may be aqueous, aqueous containing asolvent, or all organic. Streams from different stages may be combinedinto one stream or treated separately. The desired fatty and/or rosinacids and/or their soaps may be in high enough concentration or mayrequire further concentration via an evaporative concentration step 13.The water 14 from this step can be recycled back to thehydrolysis/saccharification step 5.

If the suitably concentrated pulping liquor is alkaline, it should beacidified 15 using a suitable inorganic or organic acid in order to“break” fatty and/or rosin soaps and enhance the lyophobicity of thefatty and/or rosin acids. The goal of the acidulation step is to obtainall fatty and/or rosin acids in their acid form.

Once the liquor is of suitable concentration and the fatty and/or rosinacids are predominantly in their acid form, gravity separation 16 isused to split the liquor into heavy 17 and light 18 streams. Accordingto the current invention, gravity settling can be performed simply underthe influence of the earth's gravitation or under the influence ofcentrifugation. Specially baffled separation vessels such as API orlamella settlers may be employed as well. U.S. Pat. No. 4,664,802 (Lee)discloses a liquid-liquid lamella separator suitable for use in thecurrent invention. Gravity separation may be accomplished in a suitablysized vessel equipped with weirs and/or other devices that assist inseparating the two phases. It may also be accomplished usingcentrifugation according to a variety of designs including thatdisclosed in U.S. Pat. No. 4,664,802 (Lee) incorporated herein byreference. It may also be accomplished using a lamella type separatorsuch as those disclosed in U.S. Pat. Nos. 4,664,802 (Lee) and 4,151,084(Probstein et al.). Other types of gravity separation enhancingequipment known to those skilled in the art can also be applied.

In some cases, three phases may also result with the middle layer beinga “rag layer” consisting of material from the upper and lower phases ina stubborn emulsion. If the amount of desired fatty and/or rosinmaterial in the rag layer is significant, it can be isolated separatelyand recycled back to the concentration or acidulation stage. This caneither involve performing the gravity separation in batch fashion anddirecting the rag layer to separate storage during cutting of thevessel. It can also involve an additional continuous gravity separationstage in order to separate the rag layer from the upper or lower layerdepending on which layer it exits the first stage with.

The heavy phase 17 from the gravity separation step 16 is redirectedback to the fuel lignocellulose-to-fuel-ethanol process where it isutilized or disposed of according to the normal method associated withthat process.

The fatty and/or rosin acid rich light phase 18 recovered from thegravity separation step may be of suitable composition foresterification or it may require removal of impurities or separationbetween the fatty and rosin acids. If additional impurity removal and/orfatty acid/rosin acid separation is desired, it is directed to adistillation step 19. This step can be designed to produce any number ofproducts such as pure fatty acid and pure rosin acid streams accordingto batch and continuous distillation methods known to those skilled inthe art. In general, rosin acids are higher boiling than fatty acidswhich are higher boiling that other impurities recovered at this point.

Once the fatty acids 20 and rosin acids 21 separated, if desired, andacceptably free of impurities, they can be fed to the esterification andpurification section 23. A single C1-C8 alcohol or mixture thereof 22 isalso fed to the esterification section. The method of esterification andpurification along with several variations thereof are fully describedin U.S. Pat. No. 5,536,856 (Harrison et al.) which is hereinincorporated by reference. Esterification of the fatty and/or rosinacids via the method(s) of U.S. Pat. No. 5,536,856 leads to theproduction of fuel esters and water. Depending on the degree ofsaturation of the fatty acids and the content of rosin acids, theseesters find use as fuels under various specifications includingBiodiesel and jet fuel.

A sequential block diagram of an embodiment of the invention where fattyand/or rosin acids are separated from pulping liquors via liquid-liquidextraction is presented in FIG. 2. The steps and labels corresponding tothose in FIG. 1 have the same meaning as those in FIG. 1. Thelignocellulose-to-fuel-ethanol process is identical as that in FIG. 1.Fatty and/or rosin acid recovery and esterification is the same as inFIG. 1 up to step 16. In FIG. 2, the gravity separation step 16 of FIG.1 is replaced with liquid-liquid extraction 16. The liquid-liquidextraction step 16 of FIG. 2 can be operated in batch or continuousmode. In batch mode, step 16 entails blending a predetermined amount offresh and recovered solvent with the sufficiently concentrated andacidic “pulping liquor” and agitating. After a predetermined amount oftime, agitation is ceased and the liquids are allowed to gravity settleinto two or more phases. Gravity settling can be assisted according tomethods described above or performed in the same vessel in whichagitation took place. As with the process described by FIG. 1, the heavyphase 17 is directed back to the lignocellulose-to-fuel-ethanol process.The light phase 18 will be composed of the fatty and/or resin richsolvent.

In the continuous mode of step 16, a predetermined amount of solvent isfed to a point near the bottom of a trayed or packed column relative tothe amount of concentrated and acidic pulping liquor that is fed to apoint near the top. The liquid-liquid extraction is operated accordingto methods well known to those skilled in the art in order to produce aheavy mostly solvent free phase 17, and a lighter, fatty and/or rosinacid rich solvent phase 18.

In order to recover solvent for reuse in the extraction step 16, lightphase 18 is subjected to batch or continuous distillation in the solventrecovery step 26. Normally, the solvent will be the lower boilingcomponent and will therefore be taken as the distillate in the case ofcontinuous distillation or as the first overhead product in the case ofbatch distillation. The mostly solvent free fatty and rosin acids 27forming the distillation bottoms, in the continuous case, or the productremaining in the kettle after sufficient solvent removal, is thenfurther processed to fuel esters as described above in the discussion ofFIG. 1.

FIG. 3 shows a simplified schematic of a capital efficient embodiment ofequipment suitable for performing batch extraction and solvent recoveryaccording to the invention. According to FIG. 3, evaporativeconcentration 13, acidulation 15, solvent blending with liquor,agitation, separation, and solvent recovery distillation are allperformed in the same vessel. Referring to FIG. 3, the vessel isequipped with a feed line 1 for charging it with pulping liquor,solvent, and acid. It is also equipped with a motor driven agitator 2.The vessel is equipped with a steam coil 5 and steam feed 3 andcondensate return 4 lines. The sight glass 6 in combination with thevessel's cone bottom aid in performing successive sharp layer cuts asheavy, rag, and light phase layers are removed via bottom outlet 7. Itis also equipped with a packed column 8 on its vapor line and a refluxpartial condenser 9 for providing liquid reflux back down the column toaid in performing sharp distillation cuts as solvent is distilled offinto vapor line 10. The sequence of operations is that described forFIG. 2. It should be understood that other embodiments of batchextraction and distillation are well known to those skilled in the artand in keeping with the spirit of the invention.

FIG. 4 shows a simplified schematic of a capital efficient embodiment ofequipment suitable for performing continuous extraction and solventrecovery according to the invention. In this embodiment, both solventrecovery and separation between fatty and rosin acids are accomplishedin the same column. Sufficiently concentrated and acidic pulping liquoris fed to a location near the top of extraction column 3. Extractioncolumn 3 contains packing or numerous trays in order to increaseinterfacial area between the two liquid phases and to affect stage wise,countercurrent separation. Recovered 9 and fresh solvent 2 are fed to alocation near the bottom of extraction column 3. Due to the differencein density between the solvent and liquor phases, the solvent phaserises to the top of the column exiting via stream 5 while the liquorphase falls to the bottom of the column and exits via stream 4. On itsway up the column, the solvent phase extracts fatty and/or rosin acidsfrom the pulping liquor such that stream 5 contains most of the fattyand/or rosin acids fed to the column along with the liquor in stream 1.

Fatty and/or rosin acid rich solvent stream 5 is next fed todistillation column 6. Distillation column 6 can contain trays orpacking in order to affect vapor-liquid equilibrium stage separationbetween upcoming vapor created by reboiler 11 and downcoming liquidcreated by reflux condenser 10. Due to the action of the vapor liquidequilibrium stages, pure solvent is recovered as distillate in stream 9and recycled back to the extraction column, rosin- and solvent-freefatty acids are recovered in stream 7, and pure rosin acids arerecovered in stream 8.

Various modifications to the distillation column in FIG. 4 are possible.For example, the feed to the column 5 could be heat exchanged with thebottoms from the column to improve energy efficiency. Additionally, sidestrippers and/or pump around coolers could be used to improve thesharpness of the splits between solvent, fatty acids, and rosin acids.It should be understood that other embodiments of continuous extractionsolvent recovery, and fatty acid/rosin acid distillation are well knownto those skilled in the art and in keeping with the spirit of theinvention.

A sequential block diagram of an embodiment of the invention where fattyacids are recovered from concentrated algal pastes is given in FIG. 6.Algal paste 1 is obtained by any appropriate method in a concentrationof about 15% solids or more. Alkali such as NaOH is added in order toproduce a high pH mixture. The High pH mixture is subjected to heatingand agitation 2. After some time, the high pH solution is diluted withwater and allowed to settle into aqueous and oil layers containingsaponified fatty acids 3. The oil layer is skimmed and then acidulated 4with an acid such as H₂SO₄. That and subsequent heating and agitationare used to “break” the soaps 5 and yield fatty acids and salt water.The fatty acids from the soaps are recovered as an oil layer on top of asaltwater layer via settling and skimming 6. The cation free fatty acidsare then esterified according to the method of the invention 7.

The above examples are for illustrative purposes only and are not meantto be limiting. Various embodiments of the invention wherein allcomponents listed above may or may not be used are possible under thecurrent invention. All references are incorporated by reference in theirentirety.

1. A process for the production of biodiesel from a concentration ofalgae, the process comprising: i) comminution of the concentration; ii)production of an organic layer comprising fatty acid soaps; iii)acidulation of the organic layer to produce free fatty acids; iv)heterogeneous esterification of the fatty acids with alcohol to producean ester; and v) refining of the resulting ester to produce anester-based fuel.
 2. The process according to claim 1, wherein,following production of the organic layer, any residual material isfurther processed in fermentation and purification steps to yieldethanol.
 3. The process according to claim 2, wherein the ethanolproduced from the residual material makes up a substantial amount of thealcohol of step iv.
 4. The process of claim 3, wherein the alcohol is aC1-C8 alcohol.
 5. The process of claim 1, wherein said comminutioncomprises solid or liquid shearing.
 6. The process of claim 1, whereinsaid organic layer is produced via alkali lysing of the concentration.7. The process of claim 1, wherein the organic layer comprises fromabout 30-40% fatty acid soaps.
 8. The process according to claim 1,wherein said esterification occurs via a gas sparged, slurry form ofheterogeneous reactive distillation in a reaction chamber.
 9. Theprocess according to claim 8, wherein the gas sparged, slurry form ofheterogeneous reactive distillation includes free particulate acidic ionexchange resin catalysts to catalyze esterification.
 10. The processaccording to claim 10, wherein the reaction chamber comprises a verticalcolumn reactor provided with a plurality of esterification trays mountedone above another, wherein the esterification trays are adapted to allowliquid phase to pass down the column reactor and vapor phase to pass upthe column reactor.
 11. The process according to claim 10, wherein thereaction chamber comprises a vertical column reactor provided withstructured packing wherein the packing is adapted to support catalyst atone or more points in the reactor and to allow liquid phase to pass downand vapor phase to pass up the column reactor.